I had the same problem with my S2 IS. When I found out that this is a widespread issue with this model, I approached the Canon service center. They charged me Rs 225 for the problem analysis and were demanding Rs 9700 for the actual repair. Naturally, I refused to get it repaired. I even wrote a letter to some people in Canon without getting any response. I don't have the full details right now (this happened in Jan 2008) but I can post them on Friday night or Saturday morning when I get back home.